Physicochemical properties of maltosyl and glucosaminyl derivatives of beta‐lactoglobulin

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Abstract
Maltosyl and glucosaminyl derivatives of beta‐lactoglobulin (b‐LG) were analyzed for their physicochemical properties: reduced viscosity, ultraviolet difference spectra, intrinsic fluorescence, hydrophobicity and circular dichroism. The viscosity of these derivatives increased as the mass of the carbohydrates covalently linked to b‐LG increased. The ultraviolet difference spectra and the intrinsic fluorescence of these proteins revealed that the microenvironments of aromatic amino acid residues of b‐LG were increasingly exposed to the surface of the protein as the extent of modification increased; and the polarity of these residues also increased as modification increased. The hydrophobicities of M‐b‐LG derivatives decreased as the extent of modification increased while the hydrophobicities of G‐b‐LG derivatives were relatively unchanged. The circular dichroic analysis of these proteins indicated that the ordered secondary structures of the extensively modified derivatives of b‐LG were partially unfolded. Thus, the carbohydrates covalently linked to b‐LG altered many physiochemical properties. These physicochemical changes of b‐LG apparently resulted from an alteration of forces stabilizing the structure of the protein.